1. Field of the Invention
This invention relates to a hydrophilic polar group-containing polyisocyanate curing agent for a laminate adhesive, to a laminate adhesive comprising the same, and to use of the laminate adhesive in film lamination.
2. Related Prior Art
Recently, as a packaging method, a complex flexible packaging has been remarkably developed for reasons such as strength of package, protective properties for commercial product, workability during packaging, propaganda effect of package, reduction of packaging cost caused by the supply of a large amount of film at a low cost, and the like.
As an adhesive used in film lamination in such complex flexible packaging, the main product has been a two-pack curing type polyurethane adhesive composed of a resin having an active hydrogen-containing group such as a hydroxyl group or the like (main ingredient) and a polyisocyanate (curing agent) because it is excellent in bond performance, durability and heat resistance and it can be applied to various films in a broad range.
For example, JP-A-5-112,766 discloses an adhesive comprising a polyurethane resin and a polyisocyanate curing agent wherein the polyurethane resin has introduced thereinto a hydrophilic polar group. Moreover, JP-A-7-48,429 describes a polyisocyanate curing agent in which a hydrophilic polar group has been introduced into the polyisocyanate.
However, with the polyisocyanate curing agent described in JP-A-5-112,766, the use of other resins than the polyurethane resin as the main ingredient results in an insufficient adhesiveness to a metal foil, a metallized film or a polyolefin film. Furthermore, in JP-A-7-48,429, an aqueous adhesive is mentioned; however, the aqueous adhesive requires blowing water away and hence much energy becomes necessary therefor.